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Biologische Systeme und Medizin Poster: Mi., 14:00–16:30 M-P193
Small-Angle X-Ray Scattering of Lipopolysaccharide-Peptide aggregates
Jörg Howe 1 , Manfred Roessle 2 , Klaus Brandenburg 1
1 Research Center Borstel, Division of Biophysics, Parkallee 10, D-23845 Borstel, Germany
– 2 EMBL Outstation Hamburg, Notkestrasse 85, D-22603 Hamburg, Germany
Bacterial endotoxin (Lipopolysaccharide, LPS) is the major component of the outer
leaflet of the outer membrane in Gram-negative bacteria. It is composed of a hydrophobic
moiety called lipid A and a hydrophilic saccharide part composed of different sugars,
depending on the bacterial species. During cell division or cell death, LPS can
be released from the membrane causing a variety of biological effects. The reaction
may be beneficial at low concentrations, but can lead to patho-physiological effects at
high concentrations like septic shock syndrome and multiorgan failure. Due to this fact,
treatment of bacterial infections with conventional antibiotics without inactivating LPS
has to be replaced by a medication that kills the bacteria and neutralizes LPS. One
possible strategy for the development of new drugs is the use of antimicrobial peptides,
which are derived from the binding epitopes of natural antimicrobial proteins.
We used the endotoxin-binding protein of the horse-shoe crab Limulus polyphemus to
synthesize peptides and tested them for their antimicrobial and endotoxin-neutralizing
properties.
LPS, as an amphipathic molecule, forms in aqueous solution three-dimensional aggregates.
The three-dimensional aggregate structure was investigated using small-angle
x-ray scattering. It was found that the biologically active form of the LPS molecules
are cubic or unilamellar structures. We found that the best peptides for neutralizing
LPS lead to a change in the LPS aggregate structure, from a cubic to a multilamellar
arrangement of the molecules.
Several other techniques are used to investigate the reaction of these peptides with
the LPS, like freeze-fracture electron microscopy and Fourier-transform infrared spectroscopy
to analyse the gel to liquid crystalline phase transition of the acyl chains
of the LPS and the influence of the peptides. Complementary, isothermal titration
calorimetry measurements were performed to get informations about the binding stoichiometry
and binding enthalpies. Our results should lead to a better understanding of
the mechanism of LPS neutralizing and lead to the estimation of necessary properties
of peptides, which effectively kill bacteria and neutralize LPS.